WASHINGTON — A nationwide survey shows that more than half of the country’s rivers and streams are in poor biological health, unable to support healthy populations of aquatic insects and other creatures.

The survey, released Tuesday by the EPA, sampled nearly 2,000 locations in 2008 and 2009 — from rivers as large as the Mississippi to streams small enough to wade in.

It found that the nation’s rivers and streams are being polluted by high levels of the nutrients phosphorus and nitrogen, which wash into them from farms, cities and sewers. They’re also threatened by development.

Conditions are worse in the East. More than 70 percent of streams and rivers from the Texas coast to New Jersey were in poor shape. Streams and rivers are healthiest in Western mountain areas.